X-rays from a rare type of supernova in the
Whirpool Galaxy were recently observed, thanks to the
fine resolution of NASA's Chandra X-ray
Observatory. The team of researchers also detected
a large number of point-like X-ray sources due to black
holes and neutron stars in binary star systems.

Chandra's image highlights the energetic central
regions of the two interacting galaxies, NGC 5194
(center) and its smaller companion (upper left) NGC
5195, that are collectively called the Whirlpool
Galaxy.

The inset contains an expanded image of the central
region of NGC 5194. Extending to the north and south of
the bright nucleus are clouds of multimillion-degree
gas, with diameters of about 1500 light years and 500
light years, respectively. The similarity of these
features with ones observed at radio wavelengths
suggests that the gas is heated by high-velocity jets
produced near a supermassive black hole in the nucleus
of the galaxy.

On the lower left of the inset image is a faint source
identified with a supernova discovered in 1994 by
amateur astronomers in Georgia, and subsequently
determined to be an unusual Type Ic supernova. The
massive stars responsible for these supernovas are
thought to have lost their outer layers of hydrogen and
helium gas thousands of years before the explosion,
either through evaporation or transfer to a
companion.

In the millennia before a doomed star explodes into a
supernova, it loses mass. X-ray observations of the
supernova shock wave provide a method to sensitively
probe into this process. The Chandra data from SN 1994I
and its surrounding area indicate that the progenitor
star evaporated material into a cloud around the star
that has a diameter at least 0.2 light years. Further
monitoring over the years will tell just how large the
cloud is, and how long the star was losing mass before
it exploded.

Andrew Wilson of the University of Maryland, in
College Park, was the principal investigator for the
Chandra observations of M51. Other scientists involved
in the research were Yuichi Terashima of the University
of Maryland, and Stefan Immler of the University of
Massachusetts, Amherst.